1. Field of the Invention
The present invention relates to a method for measuring suspended particulate matter existing in the atmospheric air.
2. Description of the Related Art
Suspended particulates in the atmospheric air, the diameter of which is not more than 10 μm, are referred to as suspended particulate matter (SPM). Although this suspended particulate matter contains mud which has been rolled up, it primarily contains black smoke, unburned fuel and sulphur compound. In the Kanto District, 35% of them has been exhausted from Diesel engine cars. It is said that those black smoke, unburned fuel and sulphur compound are seriously injurious to human's health. Especially, particulate matter contained in exhaust gas discharged from Diesel engine cars is referred to as DEP. Particulate matter, the particulate diameter of which is small, that is, the particulate diameter of which is not more than 2.5 μm, is referred to as fine particulate matter (PM 2.5), into which investigations have been energetically made in Europe and America. In the case of this PM 2.5, suspended particulate matter is mainly composed of gas exhausted from Diesel engine cars.
Concerning the method for measuring the suspended particulate matter, the following methods are known. When the atmospheric air is sucked on the ground and made to pass through a filter, suspended particulate matter is collected by the filter and observed through a microscope so as to check the profiles and the number of particulates. Alternatively, suspended particulate matter contained in the atmospheric air of a constant volume is collected by a filter by the same method as described above, and the weight of the filter before collecting the suspended particulate matter and the weight after collecting the suspended particulate matter are measured so as to find a quantity of particulates. Alternatively, suspended particulate matter collected by a filter in the same manner is subjected to an appropriate pretreatment, and chemical substance contained in the suspended particulate matter is identified with a gas chromatograph mass spectrometer, a liquid chromatograph mass spectrometer or a spectral analyzer.
In this connection, when the related-art measuring method is adopted in which suspended particulate matter is collected by a filter so as to conduct various measurements on the suspended particulate matter, the following problems may be encountered. For example, in the case of observing particulates through a microscope, images of the particulates become unclear being affected by the filter image in the background. Therefore, it is difficult to observe the image of the particulates.
Further, in the case of measuring a quantity of particulates by measuring the weight of a filter before collecting suspended particulate matter and also by measuring the weight of a filter after collecting suspended particulate matter, since the filter usually tends to absorb water, errors tend to be made by a difference between a quantity of water absorbed before collecting suspended particulate matter and a quantity of water absorbed after collecting suspended particulate matter.
Furthermore, it is difficult for suspended particulate matter, which has been collected by a filter, to exist alone. Accordingly, it is difficult for a single particulate to be irradiated with electromagnetic waves. Therefore, it is difficult for the suspended particulate matter to be subjected to spectral analysis. Further, it is difficult to extract the suspended particulate matter from the filter. Accordingly, it is difficult for suspended particulate matter to be subjected to gas chromatograph mass spectrometer.
Furthermore, according to the related-art method for measuring suspended particulate matter, the suspended particulate matter is collected on the ground. Therefore, only the suspended particulate matter existing close to the ground can be measured.